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Telescopes Branch
Structure Current Limit Violation on Day 2003/036

On DOY 2003/036 at approximately 12:25 GMT (7:25 am local), the structure current flagged out of limits high between 1.4 to 1.6 amps. The nominal high limit is 1.20 amps. Preliminary analysis indicated that the flagging of the structure current appears to coincide with the opening of the -E trim relay in SA section 3 during trickle charge. EPS SEs have since noticed these occurrences in each trickle charge period at approximately 15:38 GMT, 17:15 GMT, and 18:50 GMT.

At the first anomaly investigation meeting at 10:00a the Institute got the action to:

The latter analysis, carried out by Ron Gilliland, Daniela Calzetti, Paul Goudfrooij, and Anton Koekemoer showed that data taken by ACS< NICMOS, STIS and WFPC2 were all nominal.

The anomaly repeated in seven orbits, then stopped suddenly and the structure current returned to its normal behavior.

The most likely interpretation, according to Dave Haskins, is that a particle hit the solar array (Section 3) and created a graphite spray which generated a soft short under a particular solar array configuration (hence the orbital recurrence); the short burned itself off after seven occurrences, self-healing the array.

All systems are now nominal, and there is no measurable impact of the event on the output of the solar arrays.

Compiled from information by Manfred Miebach